module-info platform dependencies

[Mark Reinhold]

> Date: Thu, 14 May 2009 13:50:44 -0700
> From: jonathan.gibbons at sun.com

> Could you (briefly) outline your current ideas regarding platform
> specification in the module-info file. You alluded to some ideas when I
> saw you in your office earlier this week.  If you have a tangible
> proposal, I'll see what I can do to accomodate it in javac.

Sure.

The basic idea is that the compiler can ask Jigsaw whether a particular
dependence is upon a known, available platform or profile module, and it
can also ask what the default is.  If a module-info file declares at
least one dependence upon a platform module then the compiler does
nothing.  If it does not declare such a dependence then the compiler
inserts a dependence upon the default.

The org.openjdk.jigsaw.Platform class already contains a method to tell
whether a module name is that of a platform module; it would be trivial
to add another to return a module-id query for the default.  (The present
addPlatformDependenceDefault method isn't really suitable; it assumes
that ModuleInfo objects are mutable, which they shouldn't be but are
temporarily so that the current configuration-time defaulting mechanism
can work.)

So from the compiler's point of view the API would be something like:

    public class org.openjdk.jigsaw.Platform {
        boolean isPlatformModuleName(String mn);
        ModuleIdQuery defaultPlatformModule();
    }

There is a latent security issue here -- we need to ensure that platform
modules really are, well, platform modules.  That's a problem for the
runtime code, however, not the compiler.

- Mark